Instability, the driving force for new physical phenomena


Zhong, Zhicheng (2011) Instability, the driving force for new physical phenomena. thesis.

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Abstract:In chapter 2 and 3, using first-principles density functional theory (DFT) calculations, we
begin our study of LaAlO3|SrTiO3 (LAO|STO) by reproducing the band insulating states of
bulk LAO and STO with a cubic perovskite structure. In the case of LAO thin films grown
on STO substrates, alternate stacking of positively (LaO+) and negatively (AlO2-) charged
layers on the non-polar STO substrate would give rise to a huge effective internal electric
field if both materials kept the initial state and nothing else were to happen. The
accompanying electrostatic potential would diverge with increasing thickness of LAO,
leading to a polar instability. We demonstrate the internal electric field in terms of core level
shifts calculated within DFT that are consistent with a parallel plate capacitor model.
In chapter 4, we find a strong position and thickness dependence of the formation energy of
oxygen vacancies in LAO|STO multilayers and interpret this with an analytical capacitor
In chapter 5, using first-principles density functional theory calculations, we predict
GdFeO3-like rotation of TiO6 octahedra at the n-type interface between cubic pervoskite
LAO and STO.
In chapter 6, We predict a transition from the bulk planar structure to a novel chain-type thin
film accompanied by substantial changes to the electronic structure for a SrCuO2 film
thinner than five unit cells thick.
In chapter 7, We have used first-principles calculations to determine a magnetic phase
diagram of La[O1−x Fx]FeAs as a function of the doping δ, the FeAs in-plane lattice constant
a, and the distance d between the Fe and As planes.
In chapter 8, We propose an explanation for the spin Seebeck effect in terms of the
magnetization potential associated with the thermally induced magnetization gradient, which
has so far been neglected.
Item Type:Thesis
Science and Technology (TNW)
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